Technical specifications of Long Term Evolution (LTE) have been developed by the 3rd Generation Partnership Project (3GPP), which is the standardization organization of the Wideband-Code Division Multiple Access (W-CDMA). LTE is a standard that is further evolved from the High Speed Packet Access (HSPA), which is evolved technology of the W-CDMA. LTE provides high-speed communication where a downlink transmission rate of 100 Mbps or more is achieved and an uplink transmission rate of 50 Mbps or more is achieved. LTE improves latency and spectral efficiency.
For LTE, transmission power control (TPC: transmission power control) may be performed in a manner such that, as a path loss becomes smaller, a received Signal to Interference Ratio (SIR) becomes greater. Such power control is referred to as “Fractional power control (Fractional TCP).”
Additionally, for LTE, it is expected that closed loop transmission power control is utilized together with open loop transmission power control.
When the open loop transmission power control is performed, user equipment measures the path loss based on a downlink signal from a base station (eNodeB), such as a downlink reference signal. The user equipment determines transmission power based on the path loss.
When the closed loop transmission power control is performed, a base station (eNodeB) estimates a path loss based on an uplink signal. Depending on the path loss, the base station (eNodeB) sets a target SIR. The base station (eNodeB) measures a received SIR based on an uplink signal from the user equipment. The base station (eNodeB) controls the transmission power so that the received SIR becomes equal to the target SIR. Specifically, the base station (eNodeB) transmits a transmission power control command (TPC Command).
The transmission power control command indicates that the transmission power is to be increased or to be decreased.